An oven generally includes a cooking cavity configured to receive food items for cooking. The oven also includes a heating element, which can be an electric resistance element or a gas burner, for generating heat energy to cook any food items placed within an oven cavity. Some ovens may include an air blower, such as a fan, for forcing movement of heated air within the oven cavity, and those ovens are commonly referred to as convection ovens. Although convection ovens that have the ability to introduce moisture into the heated air stream are commonly referred to as “combi” ovens, the term convection oven used herein is understood by those skilled in the art to include both convection and combi ovens.
When cooking in a typical convection oven, heated air within the cooking cavity is circulated by a fan. The fan initiates a flow of heated air by pulling air in a generally horizontal direction from the cooking cavity through one or more openings (“return air openings”) which are typically disposed on a rear wall of the cooking cavity. After being heated by a heating element, the heated air is forced by the fan into the cooking cavity through one or more of the walls of the cook cavity, such as the left and right side walls. The heated air moves through the cooking cavity in a generally horizontal direction to help distribute heat energy to food articles placed within the cooking cavity. An example of the heating system of a typical convection oven can be found in U.S. Pat. No. 4,395,233 to Smith et al.
Air impingement is a special form of convection cooking whereby air enters the cook cavity through openings (“air inlets”) in one or more flat panels (“jet plates”) typically disposed along the top and bottom walls of the cook cavity. These openings are typically in the form of small holes (e.g., 0.5 inch in diameter) placed in such a way that the heated air moving through adjacent holes forms adjacent air columns directed towards the upper and lower surfaces of food articles placed in the cooking cavity. In order to increase the rate of heat transfer from these columns of heated air to the food, such air is typically moving at a higher velocity than the air moving in typical convection ovens. However, these columns of rapidly moving heated air would cause spotting on the food surface if the food were not moving relative to the jet plates. An example of the heating system and food movement of a typical air impingement oven can be found in U.S. Pat. No. 4,679,542 to Smith et al.
A plurality of linearly extended air inlets may reduce or eliminate spotting in ovens where reduced cook times are desired but food is not moved relative to the jet plates. However, in order to provide the necessary level of air velocity and directionality, the linearly extended air inlets need to have a significant vertical dimension, substantially increasing the height or size of the oven, which is not desirable for commercial kitchens where convection ovens are most often used. An example of linearly extended air inlets with significant vertical dimension can be found in U.S. Pat. No. 8,026,463 to McKee et al.
Linearly extended air inlets without significant vertical dimension, such as an array of parallel slots in a jet plate, have severe limitations. For example, as illustrated in FIG. 1, a jet plate 100 has a plurality of air inlets 101, each in the form of a narrow slot having two substantially parallel edges 102 of equal length. One problem of using a narrow slot in a jet plate to introduce air into the cooking cavity is that air frictions generated at the edges of a narrow slot reduce the volume of the air passing through the slot. However, widening the slot to increase the air volume would then reduce the velocity of the air passing through, thereby decreasing cook speed.
Another problem of using a slot as an air inlet is that, because air passes through an opening in a relatively thin plate, the slot by itself cannot provide the level of air directionality that may be necessary to penetrate the temperature gradients (boundary layers) surrounding the food articles being cooked in the cooking cavity. Accordingly, a convection oven using slots as air inlets is not effective in accelerating the cooking process in the cooking cavity.
In addition, there may be other forces in the cooking cavity that can affect the air passing through slots and cause unevenness in the distribution of air flow within the cooking cavity. For example, return air openings can cause unevenness in the air flow distribution within the cooking cavity because the areas proximate to the return air openings attract more air flow compared to other areas within the cooking cavity. In another example, a gradient of air pressure within the air plenum can cause unevenness in the air flow distribution within the cooking cavity because a portion of the air plenum having a higher air pressure forces more air flow into the proximate area within the cooking cavity. The unevenness of air flow distribution within the cooking cavity caused by these forces cannot be easily eliminated in a convection oven that uses slots as air inlets. As a result, food items placed in the cooking cavity in such a convection oven may be cooked unevenly.
Consequently, it would be desirable to provide a convection oven using improved air inlets that can eliminate the above-mentioned problems.